[Cryptography] Asymmetric encryption analogy (vault with 2 different locks)

[Jerry Leichter]


> ….This, of course, overlooks the concept of _signing_ using asymmetric
> cryptography, which requires a somewhat different description, but
> that doesn't (at least immediately) map to a physical vault either, so
> no great loss there.
Not really.  In your padlocks-as-public-keys example, all you need to change is that the padlock itself is only accessible to the signer, while the key is available to anyone.  In fact, this has a classic real-world analogy in stamped wax seals:  Only the holder of the (presumed unique and unduplicatable) stamper can attach the signing seal, but anyone can check it.  Even today, such physical seals, in more modern forms, continue to be used.  (Some very high-tech ones were developed for nuclear treaty verification.)

No analogy is perfect, and the fact that the exact same mechanism can be used for both encryption and signing is hard to realistically replicate in the physical world; but really that’s not essential anyway.  What’s actually much harder to explain in physical terms is cryptographic hash functions….

                                         -- Jerry